1. Field of the Invention
The present invention relates to an imaging element and more particularly to an imaging element and an imaging device that can store a signal charge generated by a photoelectric conversion and read the signal charge at a desired timing.
2. Description of the Related Art
As the related art CMOS image sensor, a structure of a pixel equivalent circuit shown in FIG. 4 is known. As shown in FIG. 4, the CMOS image sensor uses a scanning type reading system that a signal charge generated in a photodiode is read in order one pixel by one pixel. In the case of this system, when an image of a moving object to be shot is picked up, the picked up image is disadvantageously distorted due to the shift of an exposure time between the pixel whose turn of reading is early and the pixel whose turn of reading is late in an imaging area.
To solve the disadvantage of the scanning type reading system, as disclosed in ITE Technical Report vol. 30 No. 25 pp 25-28, a method is proposed that a reading speed is increased to increase a frame rate so that the shift of an exposure time between pixels is decreased to reduce the distortion of a picked up image.
On the other hand, in a CCD image sensor, since a reset operation of a photodiode is simultaneously applied to all pixels and a reading operation from the photodiode to a charge transfer path is also substantially simultaneously carried out, the synchronization of an exposure time between the pixels is established (especially, a progressive scanning CCD). In the CMOS image sensor, as disclosed in JP-A-2006-148104, a function can be realized for temporarily storing a signal charge in a storage part and reading the signal charge at the same timing by providing the storage part having a light shielded in a pixel.
However, in the CMOS image sensor, a structure that the storage part is provided for storing the signal charge requires an element having the same electrostatic capacity as that of the photodiode for generating the signal charge. Since this structure is disadvantageous in a CMOS circuit at the time of micronizing a pixel, the structure is not ordinarily employed.